This error means that WinBackup has been unable to backup a file due to it being open already by another user or application (such as Outlook when backing up e-mail). This may also happen because the file is a system file such as pagefile.sys or the current user does not have sufficient privileges to access the file. Review the full warning message to find out what file caused this problem. If you do not have sufficient privileges to access the file, please contact your system administrator to award you these rights.
Looking at the particular warning given in WinBackup should lead to resolving the issue. In most cases, the warning relates to a file that is in use such as a Word document. It is recommended that you close all your applications when performing backups to avoid unnecessary problems.